For Mac OS versions up to 10.14 Mojave, you'll want iMovie 6.5.1...
Apple's simple and very user-friendly video editor. A user-modified version that works up to late Intel machines. The last version of...
www.macintoshrepository.org
It's an unofficial build that updates it to run on newer Mac OS version with 32-bit application support. I've used it on said operating systems with minimal hassle...
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While it's a fun throwback, for similar editing features and power, I generally use the modern Final Cut Pro. (Seriously, it even has many of the same video effects iMovie HD 6 had, but even better because you can control them with keyframes! Final Cut even has DVD chapter marks.)